A spark plug used for an internal combustion engine or the like includes, for example, a center electrode extending in an axial direction, an insulator provided around the center electrode, a tubular metallic shell provided around the insulator, and a ground electrode joined to a front end portion of the metallic shell. The ground electrode is bent such that its distal end portion faces a front end portion of the center electrode, whereby a spark discharge gap is formed between the front end portion of the center electrode and the distal end portion of the ground electrode.
In recent years, there has been proposed a technique of resistance-welding a tip formed of a metal which is excellent in erosion resistance (e.g., iridium alloy, platinum alloy, or the like) to a part of the distal end portion of the ground electrode, which part forms the spark discharge gap, to thereby improve not only ignition performance but also erosion resistance (see, for example, Japanese Patent No. 3980279 “Patent Document 1”, etc.).